<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>下拉框回显</title>
    <script src="/static/jQuery-1.11/jquery-1.11.3.min.js"></script>
</head>
<body>
<select id="s1">
    <option value="1">选项1</option>
    <option value="2">选项2</option>
    <option value="3">选项3</option>
    <option value="4">选项4</option>
    <option value="5">选项5</option>
</select>
<br/>
<input type="button" value="回显第3个选项" onclick="echo();"/><br/>
<script>
    function echo() {
            console.log($("#s1 > option:eq(2)").prop("selected",true))
    }
</script>
</body>
</html>